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1. Field of the Invention
This invention generally relates to connection admission control in a communications network. In particular, the invention relates to control methods and systems for admitting additional connections to a virtual path.
2. Description of the Prior Art
Various communications networks, such as Broad Band Integrated Services Digital Networks (B-ISDN) using Asynchronous Transfer Mode (ATM), are designed to ensure quality of service to users while attempting to maximize allocation efficiency of network resources. To maximize efficiency, the usage of available bandwidth within the network is maximized, which may result in a lesser quality of service.
Connection admission control (CAC) assists in efficient bandwidth utilization while maintaining quality of service. CAC is also used for the allocation of buffer resources associated with establishing new connections to a network. The Techniques for determining available bandwidth used for CAC may also be used for dynamic bandwidth control (DBC) where network resources, such as bandwidth and buffers, may be continually monitored and reallocated from underutilized paths to overutilized paths. In an ATM communications network, virtual connections are established to provide 53 byte packets or cells along virtual paths through the communications network. In these networks, CAC operations are performed when a virtual connection or virtual path is established, such as by accepting or rejecting a requested virtual connection to the network. The CAC strategy used may vary based on the type of network, such as an edge-core network where CAC processes are performed at edge switches or a step by step process where CAC is performed at each switch along the path. However, none of the various CAC methods are fully effective at handling variable bit rate (VBR) traffic.
In many CAC schemes, user-provided traffic parameters, such as peak and sustainable cell rates, are evaluated based on various assumptions to admit or deny a requested connection. For example, if the evaluated parameter exceeds an available bandwidth associated with a virtual path, the request to establish a connection is rejected. However, the evaluation of the traffic parameters may or may not accurately represent the cell arrival process associated with a requested virtual connection. Traffic parameters may not be unique to specific cell arrival processes, and the user may provide inaccurate traffic parameters. Inaccurate traffic parameters may result in under utilization or over utilization of the connection. Over utilization may result in lower quality of service where many cells are tagged as low priority.
Specific approaches to CAC include static and dynamic methods. For static methods, a user provided traffic parameter is applied to a model as discussed above. Once allocated, any resources to support the connection are left undisturbed for the life of the connection. For example, an end-to-end virtual path CAC method using a weighted round robin (WRR) queue serving has been proposed by K. Liu et al. (xe2x80x9cDesign and Analysis of a Bandwidth Management Framework for ATM Based Broad Band ISBNxe2x80x9d), IEEE Communications Magazine, May 1997, pp. 138-145. Other static approaches with varying levels of bandwidth utilization include peak rate allocation, equivalent capacity or equivalent bandwidth where bandwidth for admission is determined as a function of the bursty nature of the traffic and an acceptable cell loss ratio where, cell loss probability (probability equations used to establish a cell loss requirement), and fast resource allocation (controlling cell admission rather than connection admission).
Dynamic CAC methods typically rely on a measurement, allowing CAC decisions based on current resource utilization. Various measurements are used, such as the number of arriving cells, buffer occupancy, and the number of cells lost. Specific approaches include probability distributions of arriving cells (developing a probability distribution of arriving cells during a particular period to estimate a cell loss ratio assuming a requested connection is admitted), aggregate cell statistics (estimating bandwidth calculations or cell loss ratios based on statistic probabilities), measured buffer occupancy or virtual buffers (guaranteed fraction of cell loss ratio with renegotiation of traffic parameters), deviation rate functions (large deviation rate functions used to predict bandwidth requirements by estimating the existing load of cell arrivals and prediction of the bandwidth required based on the user-declared traffic parameters), and measurement of end-to-end delay (derives buffer and connection resources in use by measuring transmission times). Fuzzy logic and neuro-network approaches have also been proposed. However, many of these methods of CAC rely on estimates of statistical characteristics of the traffic or estimate certain parameters of the network, which may result in underutilized bandwidth. Furthermore, various methods, such as the deviation rate functions, are computationally complex and are carried out for each switch along a virtual path, requiring a step-by-step CAC process as each connection proceeds through the network.
Other dynamic CAC techniques are based on end-to-end virtual path architectures. However, these methods require a measurement of cell arrivals at every connection in a path. See for example, K. Liu et al. (xe2x80x9cA Measurement-Based CAC Strategy for ATM Networksxe2x80x9d), Proceedings of IEEE ICC""97, 1997.
The present invention is directed to improvements that more efficiently utilize bandwidth based on measurements that may be more accurate and efficient.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiment of the present invention described below is directed to a system and method for connection admission control using virtual path empty cell measurement and statistically determined allowable additional bandwidth on a virtual path.
The present invention relates to improvements in the efficiency of network resource allocation. Cell time slots, such as those serving idle, unassigned or low priority cells, may be considered to be empty since they may be replaced by high priority cells. These effectively empty cell time slots (herein xe2x80x9cempty cell time slotsxe2x80x9d) are measured and used to statistically determine the allowable bandwidth. New connections are admitted if the requested bandwidth is less than the allowable bandwidth. By measuring the number of empty cell time slots transmitted on a virtual path, the bandwidth of the communications network is more efficiently allocated by statistically utilizing the results of the measurement.
In one embodiment for using empty cell time slots as a means to determine allowable bandwidth, a weighted round robin queue structure is used with a virtual path connection establishing an end-to-end path within the communications network. Empty cell time slots at one location in the virtual path may be measured. By computing the allowable bandwidth associated with the number of empty cell time slots and comparing the allowable bandwidth to the user-defined bandwidth of a requested connection, connection admission control is performed. Measurement and statistical evaluation of empty cell time slots within a virtual path mitigates inaccuracies associated with user traffic parameters and allows for simple calculations.
In a particular first aspect of the invention, a method for connection admission control in a communications network is provided. A virtual path associated with a plurality of virtual connections is established from a source switch in the communications network to a destination switch. Cells associated with the plurality of virtual connections into the virtual path are scheduled. A bandwidth associated with empty cell time slots in the virtual path at a source switch server is measured. An additional virtual connection with an associated bandwidth is admitted to the communications network and virtual path if the additional connection bandwidth is less than the calculated bandwidth associated with the empty time slots.
In a second aspect of the invention, at least a source switch and a destination switch establish a virtual path associated with a plurality of virtual connections to the source switch. A first source switch server schedules cells associated with the plurality of virtual connections into the virtual path, and a processor determines a bandwidth associated with empty cell time slots in the virtual path. A plurality of queues operatively connect to the first source switch server and each of the plurality of virtual connections. The switch admits an additional virtual connection to the virtual path if a bandwidth associated with the additional connection is less than the bandwidth associated with the empty cell time slots. The first source server and the processor may comprise a same server.
In other embodiments, additional virtual connections may be admitted only if the virtual connection bandwidth is less than a fraction of the bandwidth associated with the empty cell time slots. Furthermore, the bandwidth associated with empty cell time slots may be determined based on measurement over a plurality of weighted round robin cycles.